In conventional hard disks having a rotating magnetic medium, there is only one magnetic layer to record data. As such, the servo pattern information is recorded in servo wedges. This way of storing servo information is also known as embedded servo. FIG. 1 is a schematic 100 showing the arrangement of servo pattern information 102 along a track on the magnetic layer. Servo information 102 is interspersed with data information 104.
The position of the read/write head is demodulated from the servo wedges. Thus, the sampling frequency of the servo control system is thus limited by the number of servo wedges in one revolution, and the rotating speed of disk. To improve the servo performance, such as tracking accuracy for high track density drive, a higher sampling rate is needed, which in turn requires more servo wedges to be placed in the magnetic layer. However, this will cause less data sector to be available for recording the user data. This is undesirable.